1. Field of the Invention
This invention relates in general to wireless digital communications. In particular, the invention relates to a frequency hopping strategy for use in frequency hopping spread spectrum communications.
2. Background Art
Devices incorporating wireless communications techniques are becoming increasingly prevalent in modern society. An inevitable result of this trend is that frequency spectrums will become more crowded and increasingly prone to interference. At the same time, consumers are becoming increasingly concerned about the privacy and security of communications. Consequently, systems engineers designing a variety of wireless communications systems, including cellular and cordless telephones, are increasingly turning to digital spread spectrum signaling methods to achieve better voice quality, greater security, and more efficient bandwidth utilization than can be achieved with other signaling methods, such as amplitude or frequency modulation without bandwidth spreading.
One popular spread spectrum signaling technique is frequency-hopping spread spectrum (“FHSS”) protocols. A FHSS transceiver operates by rapidly changing its tuned carrier frequency in a known pattern, called the hop sequence or hop pattern. By using different hop sequences, multiple users can communicate simultaneously over differing communications channels all within a common frequency bandwidth. FHSS offers better voice quality than other solutions in noisy environments because when a short segment of voice data is transmitted on a “bad” channel, it is simply muted. Thus, when the number of bad channels in the hop sequence is relatively low, the resultant degradation in voice quality is not noticeable to the user.
Another aspect of FHSS systems which is particularly advantageous is the ability to circumvent static sources of interference at a particular frequency by dynamically changing the frequency channels in the hop sequence, substituting a new frequency channel for a channel that has been identified as having excessive noise. Numerous methods of monitoring channel performance and determining when a channel should be removed from the hop sequence are known in the art.
However, typical prior art FHSS systems simply randomize the entire pool of frequency channels, before selecting an initial subset of channels on which communication is to occur, thereby leaving a random pool of reserve channels ready for substitution. Thus, oftentimes adjacent channels in the hop sequence will be similar in frequency. When this occurs, a broadband source of interference could block several consecutive channels in the hop sequence. This circumstance results in greater sound quality degradation through longer periods of “muted” audio, and inhibits the data communications that are required for implementation of dynamic channel allocation techniques.